Heat Recovery for Large Scale Boilers


A common large scale or industrial use of heat recovery technology is to install it for boilers and lead to huge savings and a significant reduction in carbon footprints. Boilers work by converting the energy from a fuel, such as oil, gas, or biomass, for the purpose of heating water. The fuel is burned and the resulting heat gets transferred to the water.

During this process though, the excess gas produced by the burning of the fuel leaves the boiler through a flue or chimney. Many large scale boilers used by industrial organisations are inefficient because additional heat produced by burning fuel is lost through the flue, sometimes as much as 20%.

Types of Large Scale Boiler

There are a wide range of boilers used in industrial processes, from those that still use coal to the more energy efficient biomass boilers.

  • Coal boilers: Mainly used to heat water and produce steam, coal can be a more effective fuel for large scale concerns compared to gas or oil. Whilst it is a fossil fuel there are still a fair number of them in existence and ensuring they are as efficient as possible is a priority for most industries.
  • Bark boilers: These are mainly used in paper pulping mills and are fed back into the system to provide steam for paper production. The bark is a waste product from the process.
  • Recovery boilers: Because they have a life span of around 40 years, there are plenty of recovery boilers around but they can be updated with the latest technology to make them more efficient.
  • Gas boilers: These are normally used by large industrial concerns that have a number of applications to run. The boilers produce high powered steam to run machinery and considered one of the more economical solutions for large factories and power plants.
  • Biomass boilers: Biomass is fuel made from biological material and is one of the cleaner and more sustainable fuels.

Because of the longevity of many boilers, some of which can last 40 years or more, it’s often not just a simple case of replacing with new technology – the cost is often prohibitive and many industries opt instead to update their existing machinery with some form of heat recovery system.   

How does Heat Recovery work for Large Scale Boilers?

Large Flue Gas Heat ExchangerThe heat contained in flue gases can be harnessed through the use of what are known as ‘boiler flue economisers’. These are normally fitted to new boilers that are more eco-friendly but can be retrofitted to the flue itself, where they capture the gas in heat exchanger tubes.

Unheated water passes over the heat exchanger tubes before it reaches the boiler, warming up beforehand. This means that less fuel needs to be used by the boiler to bring the water up to the right temperature. It also reduces the effect of what is known as ‘thermal shock’, which is caused by big differences in temperature and can add to the longevity of the system. The result is that large scale boilers with a heat recovery system like an economiser can help reduce costs and keep down that all important carbon footprint.

This form of heat recovery may be suitable for a range of boiler types, though the exact configuration of the system will vary between installations.

Large Scale Condensing Boilers and Heat Recovery

There is one type of boiler that may not be suitable for flue gas heat recovery, however. Condensing boilers are highly efficient as they already involve heat recovery (up to 90% efficiency in some cases), whereby the flue gases are used to preheat the cold water before it enters the boiler, thus reducing the work the boiler needs to do.

Combining Heat Recovery with Other Technologies

As well as being suitable for oil, gas and CHP, it is also possible to combine heat recovery systems with other green or low-carbon technologies, such as wood chip boilers, onto which a flue economiser can be fitted. What’s more, specialist commercial premises may have other sources of waste heat which can be exploited, such as the exhaust air sections of certain industrial processes.

Find out more about large scale industrial heat recovery here.

What is Boiler Blowdown?

In large industrial boiler systems, water is intentionally blown out of the boiler by some force such as steam in order to prevent the accumulation of impurities and dirt in the main body of the array. The most effective way of doing this is by surface blowdown where a small amount of water is bled out the boiler and fed into a flash tank and a heat exchanger.

Modern Industrial Large Scale Boilers

It’s estimated that industry in the UK contributes around 14.7% to our carbon emissions and the battle is on to reduce our reliance on fossil fuels and also to increase our efficiency. Whilst large scale boilers need, by their very nature, to take on large and energy intensive operations, the technology to reduce the amount these systems waste is beginning to make a big difference across the country.

Heat recovery installation companies will be able to advise you on the type boiler you have and the suitability of a heat recovery system. These companies may undertake a feasibility study to better determine your site’s potential for heat recovery.

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